N° 54–1999: XMM flying beautifully

20 December 1999

The European Space Agency's new X-ray space telescope has reached its operational orbit less than a week after being launched from Kourou on 10 December. The XMM spacecraft, which is being controlled by teams at the ESA's Space Operations Centre, ESOC in Darmstadt Germany, is functioning admirably.

The early orbit phase came to an end on 16 December after XMM had been manoeuvred to its final orbit. This required four firings of its thrusters, on successive passages at apogee, in order to increase XMM's velocity, thus elongating its orbit and raising the perigee from 826 km to 7,365 km. One burn was then made to fine tune the apogee to around 114,000km. The spacecraft, being tracked by ground stations in Perth, Kourou and Villafranca, is now circling the Earth in this highly elliptical orbit once every 48 hours.

The XMM flight operations staff have found themselves controlling a spacecraft that responds exceptionally well. During these first orbits, the satellite has been oriented several times with razor-sharp precision. On board systems have responded without incident to several thousand instructions sent by controllers. "XMM is flying so beautifully" says Dietmar Heger, XMM Spacecraft Operations Manager. "The satellite is behaving better in space than all our pre-launch simulations and we have been able to adjust our shifts to this more relaxed situation".

On his return from French Guiana, Robert Lainé, XMM Project Manager immediately visited the Darmstadt Mission Control Centre, at ESOC. "The perfect behaviour of XMM at this early stage reflects the constructive cooperation of European industrial companies and top scientists. Spacecraft operations are in the hands of professionals who will endeavour to fulfill the expectations of the astronomers and astrophysicists of the world. I am very happy that ESA could provide them with such a wonderful precision tool".

During the early orbit phase, controllers have activated part of XMM's science payload. The three EPIC X-ray cameras have been switched on and vented. On 17 December the telescope doors were opened allowing the spacecraft's golden X-ray Multi Mirror modules to see the sky. The Optical Monitor telescope door was opened on 18 December. During this last weekend, XMM's Radiation Monitor which records the flux of cosmic particles and radiations was switched on.

Mission controllers have now placed XMM in a quiescent mode for the Christmas and New Year period. Full operations will resume on 4 January with the start of the spacecraft commissioning phase due to last until 15 February. ESA's XMM Science Operations Centre at Villafranca will be brought online early January allowing the start of the exhaustive calibration and performance verification phase of XMM's science instruments. Progress on this calibration should allow the telescope to target and take "firstlight pictures" of its first X-ray sources next March.